The present invention pertains to the data processing art and, more particularly, to an interface for providing communication between data processors using a minimum number of connecting lines.
In large data processing systems it is often necessary to separate data processing units by considerable distances. For example, in one computer aided design system involving real-time interactive computer graphic tools to create and design components, a plurality of satellite, or work stations, including a graphic screen, a keyboard, an alphanumeric menu display, and other support hardware and peripheral equipment all feed into a graphic central processing unit which, in turn, connects to a data management system. The data management system is in charge of file management and other functions.
The graphic central processing units and the data management system require a controlled environment (e.g., temperature, humidity, etc.), whereas the satellite work stations may be used in an office environment. Thus, the graphic central processing units and the data management system are isolated in controlled rooms, whereas the work stations are scattered throughout design areas. The distances between the controlled area and the work station locations may exceed 1,500 feet.
The problem created by such large separation distances results from the fact that the data processing units normally communicate over parallel data and control lines. For example, in the above-described computer aided design system, communication between a work station and a graphic central processing unit is accomplished over 64 data lines (32 lines in each direction), eight control lines (4 in each direction), and two ground and shield signals, resulting in a total of 74 lines bundled in one multiconductor cable. This results in a large interconnecting cable diameter having a large bend radius. Such cables are thick, stiff and hard to pull and result in excessive installation requirements.
While numerous communication interface devices, which devices reduce the number of interconnecting cables, are known to the prior art, none of these previous designs are capable of the high speed transfer of both data and control signals over single lines.